T lymphocytes known as type 1 or invariant NKT cells (iNKT cells) recognize specific lipid ligands presented by the CD1d protein, and this component of the CD1-dependent immune response is highly conserved between humans and mice. Many detailed studies in mouse models have shown that iNKT cells contribute to immune responses against pathogens, elimination of malignant tumors, maintenance of immunological tolerance and prevention of autoimmune diseases. Great progress in understanding and potentially harnessing the many immunological activities of iNKT cells has been made in recent years as a result of the identification of various forms of synthetic a-galactosylceramide (aGalCer) that specifically activate these cells. The current proposal is focused on the identification of modified forms of aGalCer that activate different cytokine patterns when used to stimulate mouse or human iNKT cells. Numerous Th2-cytokine biasing forms of aGalCer have been identified in our ongoing studies, and we propose new synthetic approaches to create additional aGalCer analogues that will include examples with tolerogenic or proinflammatory activities based on cytokine production or other effects. These compounds will be characterized in detail using assay systems to analyze both mouse and human iNKT cell responses to identify those that are most suitable to carry forward into translational studies. Using new monoclonal antibody reagents specific for CD1d/aGalCer complexes, and soluble iNKT cell antigen receptors, we will carry out a range of studies to determine the mechanisms that lead to the stimulation of markedly different patterns of cytokines by various aGalCer analogues. Studies to optimize the adjuvant properties of selected aGalCer analogues in model systems of vaccination are also proposed. These studies will increase our understanding of the mechanisms governing the regulation of the many potential activities of iNKT cells, and will contribute to development of therapeutic applications for glycolipid activators of this T cell subset.